Answer Expert Verified It contains more organic material than the subsoil and so it is darker in color. Humus is the decayed remains of the plants and animals, which breaks down in the soil by the microbes. Thus, the top layer of soil has more humus than other layers.

Subsoil is the layer underneath the surface topsoil, which consists of greater minerals and materials of iron and aluminum compounds than topsoil. The subsoil tends to be more compact than topsoil, since it does not hold any air in the soil.

Humus is the decayed remains of the plants and animals, which breaks down in the soil by the microbes. The microbes need oxygen and nutrients to breakdown the remains. Therefore, this happens more in the topsoil, than in any other soil layer. Thus, the top layer of soil has more humus than other layers.

The topsoil layer is a mixture of sand, silt, clay and broken down organic matter, called humus. Humus is rich, highly decomposed organic matter mostly made from dead plants, crunched-up leaves, dead insects and twigs. The topsoil is relatively thin but it has most of the soil’s nutrients.

Topsoil has more humus because animals live in this layer and even roots of some plants are located in topsoil which brings loads of humus and important nutrients.

Medical Definition of humus : a brown or black complex variable material resulting from partial decomposition of plant or animal matter and forming the organic portion of soil.

Clayey soil is used to make pots, toys and statues because the clayey soil has the highest water holding capacity than loamy, sandy and silt.

A HORIZON- This is the layer that we call “topsoil” and it is located just below the O Horizon. This layer is made up of minerals and decomposed organic matter and it is also very dark in color. This is the layer that many plants roots grow in.

A horizon